The present invention relates generally to guidewires for catheters and the like, and more particularly to a guidewire for use in a rotational atherectomy procedure.
Medical catheters generally comprise elongate tube-like members which may be inserted into the body, either percutaneously or via a body orifice, for any of a wide variety of diagnostic or therapeutic purposes. Such medical applications frequently require use of a catheter having the ability to negotiate twists and turns, particularly with regard to certain cardiovascular applications.
One such application, rotational atherectomy, requires manipulation of a catheter from a position outside the patient's body through extended portions of the patient's arterial system to position a cutting tip at a stenotic site. Stenosis is an abnormal narrowing of a passage or canal in the body, commonly associated with atherosclerosis, or blocking of the arteries with plaque.
Rotational atherectomy utilizes a rapidly rotating cutting tool at the distal end of the catheter for transluminal recanalization of intravascular lesions of soft or hard thrombotic or atheromatous material. The procedure is more formally known as Percutaneous Transluminal Rotation Ablation (PTRA).
One commonly used rotational atherectomy device is made by Heart Technology, Inc. and marketed under the name "Rotablator.RTM.". The Rotablator consists generally of an advancer/catheter, a guidewire, a console and a power source of air or nitrogen. Thousands of microscopic-sized diamond crystals coat the forward face of an elliptical-shaped polishing tip. With each revolution, these crystals remove tiny scoops of plaque from the artery. The cutting tip comes in a variety of sizes ranging from 1.25 mm to 4.5 mm.
The particles, much smaller than a red blood cell, are said not to present a threat of injury by lodging in the patient's cardiovascular system. During a plaque removal procedure, only a few thousandths of a pound of the tiny plaque particles are released into the bloodstream. The body's reticuloendothelial system is believed to naturally remove as much as a pound of impurities from the blood supply each month.
The diamond cutting surfaces are said to easily remove even the hardest calcified plaque. The Rotablator is said to be useful for virtually all lesion types, including long, calcified, eccentric, and distal. The patient is left with a smooth, patent lumen. Success in the rotational atherectomy procedure is defined as a lesion with less than 50% residual stenosis and a 20% absolute improvement in the luminal diameter.
In general, the catheter comprises a small diameter, triple-helix wound tubular shaft with a cutting tip on its distal end. An air turbine causes the tubular shaft and cutting tip to rotate around the guidewire and within an outer Teflon sheath at speeds of up to 200,000 rpm. The Rotablator catheter tracks over a constant 0.009-inch diameter solid guidewire. The rotational atherectomy procedure produces a smooth, polished luminal hole and is said to lessen the occurrences of elastic recoil, flaps, and vessel dissections, commonly associated with balloon dilatation.
In a typical rotational atherectomy procedure, the guidewire is transluminally inserted into the brachial or the femoral artery, and advanced to the stenotic region. The rotatable catheter is then mounted over the guidewire and advanced to the treatment site. Coronary arteries are tortuous, have many sub-branches, and often the obstruction is either located where the diameter of the artery is small or, by its very presence, the obstruction leaves only a very small opening through which a guidewire and/or catheter can be passed. Consequently, the cardiologist often finds it difficult to maneuver the guidewire or catheter, which are typically several feet long, from the proximal end. Often, the solid guidewire used in current rotational atherectomy procedures does not have sufficient flexibility at its tip to negotiate the complex system of arteries within the patient.
In contrast, guidewires currently used for percutaneous transluminal coronary balloon angioplasty applications taper from a relatively large proximal diameter down to as little as a 0.003-inch diameter near the distal end, thus permitting greater flexibility at the tip. However, using such a tapered guidewire is generally unsatisfactory in a rotational atherectomy procedure because there is insufficient strength at the thinned distal end of the guidewire to support the rotating burr. In addition, the loose spring coil segment which typically covers the tapered distal portion of the core wire in the known coronary angioplasty guidewires tends to "unwind" inside rotating atherectomy catheter.
Thus, there remains a need for a guidewire which is especially suited for procedures such as rotational atherectomy. In particular, the guidewire should preferably be constructed in a manner such that the tip is both more laterally pliable in bending than the current rotational atherectomy guidewires, and yet better able to support a rotating sleeve and cutting tip than prior tapered core wire angioplasty guidewires.